Beynon's maternal grandfather was Arthur Wellington Clah, a hereditary Tsimshian chief and a Hudson's Bay Company employee.

When his mother's only surviving brother, Albert Wellington, died in 1913, William Beynon moved from Victoria to Lax Kw'alaams at the age of 25 to assume his uncle's hereditary title, Gwisk'aayn.

Barbeau and Beynon's series of interviews with Lax Kw'alaams chiefs and elders in 1914-15 has been called by the anthropologist Wilson Duff "one of the most productive field seasons in the history of [North] American anthropology.

From 1918 to 1924, Beynon worked extensively up and down the coast, collecting museum artifacts for Sir Henry Wellcome, executor of the estate of William Duncan, the missionary founder of Metlakatla, Alaska.

From 1929 until 1956, when Beynon became ill, he continued to send Barbeau his own fieldnotes, covering every conceivable aspect of the culture and traditions of the Tsimshian, Gitksan, and Nisga'a peoples.

[7] In the early 1930s Beynon facilitated the immensely productive Lax Kw'alaams fieldwork of Viola Garfield, a doctoral student of Boas.

The Barbeau-Beynon Collection at the Canadian Museum of History had Beynon’s name subsequently added to acknowledge his contributions to this archive of work about the Tsimshian people.

Particular indigenous groups featured in this archive include the Tsimshian, Gitxsan, Wet'suwet'en, Nisga'a, Haida, Tlingit, Haisla, Kwakwakaʼwakw, Tahltan, Dakelh, and Salish.

[9] In February 2023, four reels of microfilm containing Beynon's work were found at Tea Creek Farm in Kitwanga, British Columbia, Canada.